The present disclosure relates to a semiconductor device, and more specifically the disclosure relates to a hexagonal Group III nitride semiconductor device.
Laser diodes are presently utilized in numerous technical fields, and in particular, the laser diodes are indispensable optical devices in the field of image display units, for example, televisions and projectors. In the application of laser diodes to this field, laser diodes emitting light of respective light's primary colors, i.e., red, green, and blue are typically used, and an improvement in laser characteristics are also desired.
Japanese Unexamined Patent Application Publication No. 2002-335052 discloses a nitride-based laser diode device used in a short wavelength region of about 375 nm or less and having a configuration in which a nitride semiconductor layer including Al and In is formed in one or both of two cladding layers sandwiching an active layer (a light-emitting layer). In Japanese Unexamined Patent Application Publication No. 2002-335052, for example, an n-side cladding layer and a p-side cladding layer are made of InAlGaN and AlGaN, respectively, to achieve suppression of crystallinity deterioration and an improvement in device characteristics.
Red and blue laser diodes have been already practically used, and in recent years, green laser diodes (with a wavelength of about 500 nm to about 560 nm both inclusive) have been actively developed (for example, refer to Takashi Kyono, et al., “The world's first true green laser diodes on novel semi-polar {2, 0, −2, 1} GaN substrate I”, Jan. 2010, SEI Technical Review, Vol. 176, pp. 88-92, and Masahiro Adachi, et al., “The world's first true green laser diodes on novel semi-polar {2, 0, −2, 1} GaN substrate II”, January 2010, SEI Technical Review, Vol. 176, pp. 93-96). In Takashi Kyono, et al. and Masahiro Adachi, et al., there is proposed a Group III nitride laser diode (a green laser diode) in which an n-type cladding layer, a light-emitting layer including an active layer made of InGaN, and a p-type cladding layer, that is, laser components are laminated in this order on a {2, 0, −2, 1} semi-polar plane of an n-type GaN substrate. It is to be noted that, in this specification, plane orientation of a hexagonal crystal is represented by {h, k, l, m}, where h, k, l, and m are plane indices.
In Takashi Kyono, et al. and Masahiro Adachi, et al., a green laser diode having superior crystal quality while suppressing an influence of a piezoelectric field is achieved through forming an epitaxial layer on the semi-polar plane of a GaN substrate by crystal growth. However, in a laser diode device in which a device is formed on a semi-polar plane of a semiconductor substrate, characteristics of the substrate and characteristics of the epitaxial layer formed on or above the substrate are different from those in a laser diode device in which a device is formed on a polar plane of a semiconductor substrate. Therefore, further development of laser diodes using a semi-polar plane of a semiconductor substrate is desired.